1. Field of the Invention
The present invention relates generally to a method for setting up signaling connection in a mobile communication system, and in particular, to a method for setting up signaling connection between an RNC (Radio Network Controller) and an SGSN (Serving GPRS (General Packet Radio Service) Supporting Node).
2. Description of the Related Art
Recently, because of the development of the communication industry, a service provided by a code division multiple access (hereinafter referred to as “CDMA”) mobile communication system is being developed to include multicasting multimedia communication for transmitting voice service data and high-capacity data, such as packet data and circuit data. In order to support the multicasting multimedia communication, a broadcast/multicast service is required in which one data source provides a service to a plurality of user equipments (hereinafter referred to as “UEs”). The broadcast/multicast service can be divided into a cell broadcast service (hereinafter referred to as “CBS”), which is a message-based service, and a multimedia broadcast/multicast service (hereinafter referred to as “MBMS”) supporting multimedia data, such as real-time image and voice, still image, and text.
The MBMS refers to a service for transmitting the same multimedia data to a plurality of UEs over a radio network. The UEs share one radio channel to save radio resources. The CBS refers to a service for broadcasting a plurality of messages to all UEs located in a particular service area. The particular service area where the CBS is provided can become the entire area where the CBS is provided in one cell. The MBMS, supporting both voice data and image data, requires a great number of transmission resources. Therefore, the MBMS is serviced over a broadcasting channel, because of the possibility that a plurality of services will be simultaneously provided in one cell.
As described above, in a mobile communication system, signaling procedures between respective elements for providing the MBMS service must be proposed. Therefore, in order to provide the MBMS service, the mobile communication system should define messages for the signaling procedures between the elements and types of information included in the messages. In addition, the mobile communication system must propose a procedure for updating service contexts needed to provide the MBMS service, using the information, and a procedure for setting up signaling connection by the service contexts.
A signaling procedure proposed in the conventional mobile communication system will now be described herein below.
Conventionally, Iu signaling connection is formed for an individual UE by setting up an RRC (Radio Resource Control) connection by the UE. If the RRC connection is released, the Iu signaling connection is also released: A process of setting up the Iu signaling connection will be described below with reference to FIG. 5.
Referring to FIG. 5, if an event #1 originates from a UE in step 501, an RNC 510 prepares to set up an Iu signaling connection. Event #1 is an event in which a message to be transmitted to a core network (hereinafter referred to as “CN”) 520 has arrived from a particular UE before signaling connection is set up between the UE and the CN 520. Typically, the event #1 represents an event where a particular UE sets up RRC connection with an RNC 510, and then transmits an RRC message of an Up link Direct Transfer message to the RNC 510 through the RRC connection. If the Iu signaling connection to the UE is not set up, the RNC 510 sets up the Iu signaling connection, converts the Uplink Direct Transfer message into an RANAP (Radio Access Network Application Part) message of an Initial UE Message, and transmits the RANAP message to the CN 520. The message transmitted to the CN 520 by the RNC 510 is comprised of control information of only one UE.
More specifically, if the event #1 occurs in step 501, the RNC 510 forms an Initial UE Message based on a message that caused the event #1. At this point, an RANAP 511 determines a signaling connection id (identifier) corresponding to the UE and delivers the information to an SCCP (Signaling Connection Control Part) layer 512 along with the Initial UE Message (Step 502). The SCCP layer 512 forms an SCCP message called CR (Connection Request) in accordance with Equation 1, and transmits the SCCP message to an SCCP layer 522 of a CN 520 (Step 503).CR=[LR—RNC, Initial UE Message]  (1)
The CR is a message transmitted to initially set up an SCCP connection by the SCCP layer 512 of the RNC 510, and an LR_RNC (Local Reference RNC) constituting the CR message is a temporary identifier assigned to the SCCP connection by the SCCP layer 512. After the SCCP connection is set up, the SCCP layer 522 of the CN 520 identifies the SCCP connection, using the LR_RNC constituting the SCCP message. Upon receiving the CR message, the SCCP layer 522 of the CN 520 assigns an LR_CN (Local Reference CN) by delivering an Initial UE Message included in a payload part of the CR message to the RANAP 521 (Step 504). The LR_CN is a temporary identifier for SCCP connection to be set up through the CR message.
After the SCCP connection is setup, the RNC 510 identifies the SCCP connection using the LR_CN when transmitting an SCCP message. The RANAP 521 of the CN 520 stores an Iu signaling connection id included in the received Initial UE Message, and delivers an RANAP message, if any, to the SCCP layer 522 (Step 505). However, if there is no RANAP message to send, step 505 can be omitted. The SCCP layer 522 forms an SCCP message called CC (Connection Confirm), using the LR_CN, and transmits the SCCP message to the RNC 510 (Step 506).CC=[LR_CN, LR_RNC, RANAP Message] (existing only when step 505 is performed)  (2)
The CC is a response message transmitted from the SCCP layer 522 that received the CR to the SCCP layer 512 that transmitted the CR, while a particular SCCP connection is set up.
The SCCP layers 512 and 522, which newly set up the SCCP connection, exchange the CR and the CC, thereby recognizing the temporary identifiers LR_RNC and LR_CN assigned to SCCP connection by the other party. In addition, the SCCP layers 512 and 522 include the temporary identifiers in the SCCP message when exchanging the SCCP message using the SSCP connection.
The SCCP layer 512 stores LR_CN upon receiving the CC. If a RANAP message is included in the CC, the SCCP layer 512 delivers the message to the RANAP 511 (Step 507).
A state where the RNC 510 and the UE share [LR_RNC, LR_CN, Iu signaling connection id] for particular SCCP connection through the above process is a state where Iu signaling connection is set up. Thereafter, when desiring to transmit a RANAP message through the SCCP connection or when desiring to transmit a SCCP connection-related message from a UE to the CN 520, the RNC 510 forms an SCCP message including LR_RNC and LR_CN stored together with the In signaling connection id, and delivers the SCCP message to the CN 520. The CN 520 receives an RANAP message included in the SCCP message for a UE indicated by an In signaling connection id corresponding to the LR_CN and the LR_RNC included in the received SCCP message.
FIG. 7 illustrates a process of exchanging MBMS-related RANAP messages in a conventional method. If N UEs of UE #1 to UE #N exist in a particular RNC area, each of the UEs desires to request reception of a particular MBMS service. If each UE transmits a first MBMS Service Request message to an RNC, the RNC performs an RNC Service Context initialization process and an RNC Service Context UE list update process. In succession, the RNC transmits a second MBMS Service Request message and a plurality of MBMS Service Update messages to an SGSN (or CN), using Iu signaling connections of the UE #1 to the UE #N. However, if there is no Iu signaling connection, the RNC sets up new Iu signaling connection for the corresponding UE, and then transmits the MBMS-related RANAP messages to the SGSN.
Referring to FIG. 7, if an RNC receives a first MBMS Service Request message from a UE #1 in step 701-1, it performs a necessary operation such as RNC Service Context initialization to determine whether an event #1 situation has occurred. That is, the RNC determines whether In signaling connection has already been set up for the UE #1. If the Iu signaling connection has already been set up, the RNC transmits a second MBMS Service Request message to an SGSN, using the set Iu signaling connection in step 702-1.
If the RNC receives a first MBMS Service Request message from the UE #N in step 701-N, it performs a necessary operation such RNC Service Context UE list updating to determine whether an event #1 situation has happened. That is, the RNC determines whether Iu signaling connection has already been set up for the UE #N. If the Iu signaling connection has already been set up, the RNC transmits an MBMS Service Update message to the SGSN, using the set In signaling connection, in step 702-N. However, if the Iu signaling connection is not set up, the RNC sets up Iu signaling connection for the UE #N, and then transmits the MBMS Service Update message to the SGSN. Setting up of the Iu signaling connection for the UE #N is performed by the process presented in FIG. 5.
It will be assumed that a particular MBMS service is being provided to corresponding UEs. The SGSN must notify the RNC, if the MBMS service is ended at a certain time when the MBMS service is provided. For that purpose, the SGSN delivers an RANAP message of an MBMS Service Stop message to all UEs.MBMS Service Stop=[TYPE, MBMS Identifier]  (3)
The MBMS Service Stop messages are individually transmitted to the RNC through Iu signaling connections formed for the UEs receiving the MBMS service in steps 703-1 to 703-N. In steps 704-1 to 704-N, the RNC converts the MBMS Service Stop message into an appropriate RRC message (e.g., Stop Indication message), and transmits the RRC message to the UEs.Stop Indication=[TYPE, MBMS Identifier]  (4)
As illustrated in FIG. 7, because signaling connections of related UEs are used to transmit MBMS-related RANAP messages, the same contents message such as the MBMS Service Stop message must be transmitted to all UEs undesirably.